JPH01295271A - Image forming device - Google Patents

Abstract

PURPOSE:To always stabilize the electrified potential of a photosensitive body at a desired one by controlling an electrifier based on the measured value of a potential sensor whose output is calibrated so that the surface potential of the photosensitive body can be electrified to a fixed potential. CONSTITUTION:Whenever the main switch of the image forming device, for instance, is turned on, a 1st switching means 37 is switched. In response to that switching, the photosensitive body 21 is biased to a predetermined high voltage, and the measured value of the potential sensor at that time is read out. An electrifier control means 35 controls an output from the electrifier 23 to electrify the surface of the photosensitive body, and at the same time the output of the electrifier 24 is adjusted so that the output from the potential sensor 24 can be equal to the read-out measured value. In such a way, the title device is provided with the potential sensor 24 detecting the surface potential of the photosensitive body, and a circuit automatically calibrating the output of the potential sensor at a fixed timing, whereby the output from the potential sensor measuring the surface potential of the photosensitive body can be one which is always calibrated. Thus, the photosensitive body can be electrified at a desired potential.

Description

Detailed Description of the Invention <Industrial Application Field> Regarding an image forming apparatus having a photoreceptor that forms an electrostatic image by being exposed to light, in particular, adjusting the charged potential of the photoreceptor to a constant potential before exposure. The present invention relates to an image forming apparatus that is improved so as to be able to perform the following functions.

<Prior art> As an image forming apparatus having a photoreceptor, an electrophotographic copying machine,
Laser printers, electrophotographic facsimiles, and the like are known.

Taking an electrophotographic copying machine (hereinafter referred to as a "copying machine") as an example, it is equipped with a drum-shaped photoreceptor (hereinafter referred to as a "photoreceptor drum"). The photoreceptor drum is generally made of an aluminum tube, and a photo-semiconductor layer is provided on the surface of the photoreceptor drum. During image formation, the photosemiconductor layer on the surface of the photoreceptor drum is charged to a constant potential by corona discharge from a charger, and the charged photosemiconductor layer is exposed to light, which removes the charge in the exposed area and creates an electrostatic charge there. This is the mechanism by which a latent image is formed.

However, in the optical semiconductor layer, there may be variations in the way charges are carried depending on the location, and it may be necessary to adjust this.

Conventionally, in the manufacturing process of a copying machine, a jig was used to check how the charge was applied to the optical semiconductor layer, and if it was not constant, it was adjusted.

Another method is to incorporate a potential sensor that measures the potential on the surface of the photoconductor drum, and feed back the measured value of the potential sensor to the control circuit of the charger that charges the surface of the photoconductor drum. Some are designed to hold constant.

However, when a potential sensor is provided to measure the potential on the surface of the photoreceptor drum, it is necessary to calibrate the output of the potential sensor for the following two reasons.

The reasons for this are: ■ The sensitivity of each potential sensor varies, and ■ When a potential sensor is mounted opposite the photoreceptor drum surface, the distance between the drum surface and the potential sensor varies slightly depending on the product. That is.

By the way, when calibrating the output of the potential sensor, apply a predetermined high voltage directly to the photoreceptor drum, read the output of the potential sensor at that time, and calculate from the sensor output with respect to the applied voltage.
It is convenient to set calibration values.

In a conventional copying machine, as schematically shown in FIG. , a developing bias circuit 9 is connected via a connector 7 and a connecting wire 8. In such a configuration, in order to calibrate the output of the potential sensor 10, the connector 7 and the connector 3 are replaced, a predetermined high voltage is applied to the photosensitive drum 1 by the developing bias circuit 9, and the potential sensor 10 at that time is The output of the potential sensor can be read and used to calibrate the output of the potential sensor.

<Problems to be Solved by the Invention> However, with this method, the output of the potential sensor is only calibrated when the copying machine is manufactured, or only a specialized service person can calibrate the output during maintenance.

On the other hand, when a copying machine is operated, the potential sensor is often contaminated with toner or the like during use, and the sensor sensitivity gradually deteriorates. In such a case, it is also necessary to calibrate the sensor output. Therefore, if this is left as is, good copies cannot be obtained.

Similar problems have been encountered not only in copying machines but also in general image forming apparatuses such as laser printers and electrophotographic facsimile machines.

Therefore, the present invention provides a potential sensor that detects the surface potential of the photoconductor and a circuit that automatically calibrates the output of the potential sensor at a certain timing, and the output of the potential sensor that measures the surface potential of the photoconductor. An object of the present invention is to provide an image forming apparatus that can always provide a calibrated and correct output and, as a result, can always charge a photoreceptor to a desired potential.

Means for Solving the Problems> This invention provides a photoreceptor and a surface of the photoreceptor that faces the surface of the photoreceptor,
An image system that has a charger that charges the opposing photoreceptor surface to a constant potential by performing corona discharge, and an electrostatic image is formed on the photoreceptor surface that is charged to a constant potential by being exposed to light. The forming apparatus includes: a high voltage generation circuit for outputting a predetermined high voltage; a switching means for switching whether the photoreceptor is connected to the high voltage generation circuit or grounded; a potential sensor for determining abnormal stoppage of the image forming apparatus; means for storing abnormal stoppage of the image forming apparatus; timing signal output means; switching signal output means for outputting a switching signal for the switching means so that a high voltage is directly applied to the photoreceptor from the high voltage generation circuit when no abnormal stop is stored after static elimination; and charger control means for controlling the output of the charger based on the measured value of the potential sensor when the photoreceptor is brought to a predetermined high voltage by a high voltage generation circuit. It is an image forming apparatus.

In the above configuration, it is preferable that the high voltage generation circuit also serves as a high voltage generation circuit for biasing the developing device.

Further, the voltage generation circuit may also be used as a high voltage generation circuit for applying voltage to the charger.

<Operation> The switching signal output means switches the switching means at a desired timing, for example, when the main switch of the image forming apparatus is turned on. Note that at this time, if there is a residual charge on the photoreceptor due to an abnormal stop of the apparatus, the charge is removed and then switched. In response to the switching, the photoreceptor is biased with a predetermined high voltage, and the measured value of the potential sensor at that time is read. The charger control means controls the output of the charger to charge the surface of the photoreceptor, and at this time adjusts the charger output so that the output of the potential sensor becomes equal to the read measurement value.

Image forming apparatuses are generally equipped with a high voltage generation circuit for biasing the developing device or for applying voltage to the charger, so when directly biasing the photoreceptor with a high voltage, A circuit may also be used.

<Embodiment> Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 2 is a schematic mechanical configuration diagram of the image forming mechanism of a copying machine according to an embodiment of the present invention. The copying machine is equipped with a cylindrical photoreceptor drum 21, and around it are a static elimination lamp 22, a main charger 23, and a potential sensor 2.
4, a blank lamp 25, a developing device 26, a transfer charger 27, a peeling charger 28, and a cleaner 29 are arranged in order along the rotation direction A1 of the photoreceptor 21.

Further, the photosensitive drum 21 is connected to a main charger 23.
An exposure position Ex is set between the potential sensor 24 and the potential sensor 24, and the light from the optical system 30 is irradiated thereon.

A brief explanation of the operation is as follows.

During copying, the photosensitive drum 21 is rotated at a constant speed in the direction of arrow A1, and after the residual charge on the drum surface is removed by the static elimination lamp 22, the main charger 23
The drum surface is charged to a constant potential. Then, at the exposure position Ex, the light reflected by the original to be copied is applied from the optical system 30. This exposure removes the charge on the exposed portion, and an electrostatic surface image is formed on the surface of the photoreceptor drum 21. Further, charges in unnecessary portions, such as charges in portions that are not exposed due to shadows at the leading edge and side edges of the original, are removed by the blank lamp 25.

Next, toner is attached to the surface of the photoreceptor drum 21 by the developing device 26, and the electrostatic latent image is developed with the toner. The toner is transferred to the developing roller 3 provided in the developing device 26.
1 to the surface of the photoreceptor drum 21. At this time, a developing bias voltage having the same potential as the surface of the photoreceptor drum 21 is applied to the developing roller 31 in order to prevent too much toner from adhering to the surface of the photoreceptor drum 21 .

In conjunction with such operations, a paper feed mechanism (not shown) supplies the paper P, and the toner image on the surface of the photosensitive drum 21 is transferred onto the paper P by the transfer charger 27. Then, the paper P on which the toner image has been transferred is separated from the drum surface by a separation charger 28 and sent to a fixing mechanism (not shown).

Thereafter, residual toner is removed from the surface of the photoreceptor drum 21 by two cleaners, and residual charges are removed by a static elimination lamp 22.

In the above-described series of copying operations, when the surface of the photoreceptor drum 21 is charged to a constant potential by the main charger 23, if the surface potential is not charged to the desired constant potential, subsequent exposure and development may occur. As a result, the image transferred to the paper P becomes unclear.

Therefore, it is necessary to control the output of the main charger 23 so that the charged potential on the surface of the photosensitive drum 21 is always constant.

To this end, in this embodiment, the surface potential of the photoreceptor drum 21 charged by the main charger 23 is measured by the potential sensor 24 before the copying operation, and the measured value is sent to the control circuit of the main charger 23 (described later). The measured value of the potential sensor 24 is configured to feed back to the surface potential of the photosensitive drum 21 at a predetermined timing so that the measured value of the potential sensor 24 always has an accurate correlation with the surface potential of the photoreceptor drum 21. I'm trying to calibrate it.

FIG. 1 is a block diagram showing the configuration of the electrical control circuit in the above-described embodiment.

Referring to FIG. 1, the photosensitive drum 21 is normally grounded via a ground path 32. As shown in FIG. This is because, as mentioned above, the photoreceptor drum 21 is exposed to light.
This is because the surface charge on the photoreceptor drum 21 must be constantly grounded to ensure a path for the charge to escape.

The main charger 23 includes a main high voltage unit 33.
A high voltage is applied to the main high voltage unit 33, and the main high voltage unit 33 is placed under the control of a control section 35. A developing high voltage unit 34 is connected to the developing roller 31 for applying a predetermined developing bias voltage. The developing high pressure unit 34 is also placed under the control of the control section 35. The potential sensor 24 is connected to a control section 35, and the measured value of the potential sensor 24 is provided to the control section 35.

The control unit 35 includes a memory 351 and a memory 352. The memory 351 has an area A and an area B, as will be described later, and each area stores the measured value of the potential sensor 24 given above. Further, the memory 352 is made up of, for example, one bit to several bits of flags, and the flags are set when the copying machine stops abnormally.

The control unit 35 is further connected to a drive motor 36 for driving the photoconductor drum 2 and other mechanisms of the copying machine, a static elimination lamp 22, and a blank lamp 25.

One of the features of this embodiment is that a first changeover switch 37 is inserted into the grounding path 32 of the photosensitive drum 2, so that the photosensitive drum 21 is either grounded or the developing high pressure unit 34 is grounded.
It is possible to switch between the two. A second changeover switch 38 is also provided for disconnecting the development roller 31 from the development high-pressure unit 34 when the photosensitive drum 21 is connected to the development high-pressure unit 34 by the first changeover switch 37 . And the first
The changeover switch 37 and the second changeover switch 38 are configured to be switched in conjunction with each other by a relay 39 controlled by the control section 35.

FIG. 3 shows the drive motor 36 in the control circuit of FIG.
Static elimination lamp 22, blank lamp 25, relay 39
, is a timing chart showing the operation timings of the main charger 23 (i.e., the main high voltage unit 1-33), the developing high voltage unit 34, and the potential sensor 24. FIG. It is a flowchart showing control operation.

Next, the operation of the control circuit shown in FIG. 1 will be explained in accordance with FIGS. 3 and 4, particularly the flow shown in FIG. 4.

When the control unit 35 determines that the main switch of the copying machine is turned on (step S1), first, the memory 352
Based on the stored contents, it is determined whether the copying machine stopped due to an abnormality before the main switch was turned on (step S2). The stopping of the copying machine due to an abnormality is, for example, a case where the copying machine is stopped due to paper jam during copying operation.

If the copying machine stops due to such an abnormality, the flag in the memory 352 is set as described above.

When the copying machine has stopped abnormally, the control unit 35 controls the drive motor 36, the static elimination lamp 22, and the blank lamp 2.
5 for 5 seconds (step S3.S4.S5)
. As a result, even if there is a residual charge on the surface of the photoreceptor drum 21 due to an abnormal stop of the copying machine, that charge is completely removed. Note that the residual charge may be removed by turning on only either the static elimination lamp 22 or the blank lamp 25.

The reason why the residual charge is removed in this way is that if there is a residual charge on the surface of the photoreceptor drum 21 and a high voltage is applied to the -L from the developing high voltage unit 34 as described later, the charges will be superimposed and the photosensitive drum 21 will be removed. This is because the surface of the body drum may be charged to a potential higher than the desired potential.

If the copying machine is stopped normally, there is no residual charge on the photosensitive drum 2, so this charge removal operation may be omitted.

Next, the control unit 35 turns on the relay 39 (step S6). By turning on the relay 39, the first changeover switch 3
7 and the second changeover switch 38 are switched to a state opposite to that shown in FIG. In other words, the photosensitive drum 21
is connected to the high pressure developing unit 34, and the developing roller 31 is separated from the high pressure developing unit 34.

After 100 milliseconds have passed (step S7), the control unit 35
The developing high voltage unit 34 is turned on (step S8), and the developing high voltage unit 34 directly applies a predetermined high voltage to the photoreceptor drum 21, specifically, a voltage to be charged by the charging charger 23 during copying, for example, 800 volts. . The reason why there is a 100 millisecond period between turning on the relay 39 and turning on the developing high pressure unit 34 is because the relay 39 switches the first changeover switch 37 and the second changeover switch 38 within this time. This is to ensure that this can be carried out reliably.

Next, the output of the potential sensor 24 when a high voltage of 800 volts is directly applied to the photosensitive drum 21 is read, and the value (for example, 3 volts) is stored in area A of the memory 351 (step S9).

Thereafter, the control section 35 turns off the developing high pressure unit 34 (step 510), and also turns off the relay 39 (step 511). As a result, the first changeover switch 37 and the second changeover switch 38 are changed to the state shown in FIG. 1, the photosensitive drum 2 is grounded, and the developing roller 3 is connected to the high pressure developing unit .

Next, the control unit 35 turns on the drive motor 36, the static elimination lamp 22, and the blank lamp 25 (step 512),
Wait 100 milliseconds for the rotation of the drive motor 36 to stabilize (step 313), and then control the main high voltage unit 33 to turn on the main charger 23 so that its output becomes, for example, 500 microamperes (step 514). ).

Then, after 500 milliseconds have passed (step 515)
, reads the output of the potential sensor 24 and stores it in the memory 351.
(Step 516). The reason why the blank lamp 25 is turned on in step S7 is to prevent the charged charges from being developed by the developing device in a subsequent process.

Further, in step S15, the reason for waiting 500 milliseconds is to take into account the difference between the position of the main charger 23 facing the surface of the photoconductor drum 21 and the position facing the potential sensor 24. This is to wait for the surface portion of the photosensitive drum 21 to rotate to a position facing the potential sensor 24.

Next, the control unit 35 compares the stored values of area A and area B in the memory 351 (step 517),
If the value of is larger than the value of area B, the main high voltage unit 33 is controlled to increase the output of the main charger 23 by a certain amount (step 521). Conversely, if the value in area A is smaller than the value in area B, the main high voltage unit 33 is controlled to reduce the output of the main charger 23 by a certain amount (step 522). The main high voltage unit 33 then charges the main charger 2.
After increasing or decreasing the output of Step 3 by a certain amount, the processes of Steps S1.5.8], 6 and S17 are repeated again.

Then, in step S17, if the value stored in area A of the memory 351 and the value stored in area B match, or if the values fall within a predetermined approximately equal error range, the control unit 35 controls the main High pressure unit 3
3, the control output of the main charger 2B is memorized, and the main charger 23 is turned off (step S) 8). Then, wait for 1 second to elapse (step 519).
), the control unit 35 turns off the drive motor 36, the static elimination lamp 22, and the blank lamp 25 (step 520),
Finish the action. Therefore, after this, the photosensitive drum 21 can be charged to a predetermined potential by the control output of the main charging charger 23 that has been stored twice.

Here, waiting for one second to elapse in step S19 means waiting for the surface of the photosensitive drum 21 charged by the main charger 23 to face the plank lamp 20, and charging for this control operation. This is to ensure that the surface charge on the photosensitive drum 21 charged by the charger 23 is completely removed.

In the above description of the control operation, it was explained that 800 volts is directly applied to the photoreceptor drum 21 by the developing high voltage unit 34 in step S8, and the output of the potential sensor 24 at that time is read in step S9. If applying 800 volts directly to the photoreceptor drum 21 is unreasonable due to the structure of the developing high voltage unit 34 or undesirable due to wiring, the following method may be used.

That is, referring to FIG. 5, for example, 300 port (this is referred to as Xl) is applied to the photosensitive drum 21 by the developing high pressure unit 34, and the output yl of the potential sensor 24 at that time (for example, 1, It was 5 volts.)
Load. Next, for example, 500 volts (this is referred to as
For example, it was 2.4 volts. ).

Then, from the output y1 of the potential sensor 24 when the voltage applied to the photosensitive drum 21 is Xl and the output y2 of the potential sensor 24 when the applied voltage is x2, the target value x3( For example, the output y3 of the potential sensor 24 when a voltage of 800 volts) is applied may be calculated. In this case, it may be calculated using the following calculation formula (1).

In this way, it is possible to apply a voltage lower than 800 volts directly to the photoreceptor drum 2 without directly applying a voltage as high as 800 volts. This eliminates the need to increase the output performance to 800 volts by replacing parts when the high-voltage developing unit 34 originally only has a maximum output performance of, for example, 500 volts. There is no need to increase the allowable value for wiring, and the advantage is that existing equipment and wiring can be used as is.

In each of the above cases, the target value X3 applied to the photoreceptor drum 21 is determined by the potential sensor 24 applied to the photoreceptor drum 21.
The determination is made taking into consideration the dark attenuation caused by the difference between the facing position of the developing roller 31 and the facing position of the developing roller 31 . In experiments, when the potential of the photosensitive drum 21 on the surface facing the potential sensor 21 was 800 volts, the optimum potential at the developing roller 31 was about 700 volts due to dark decay.

Furthermore, in the above embodiment, the output of the potential sensor 24 is calibrated every time the main switch of the copying machine is turned on.
Although the output of the main charger 23 is controlled based on the output of the calibrated potential sensor 24, the invention is not limited thereto.
Every time a sheet is copied, the output of the potential sensor 24 is calibrated, and the main charger 2 is calibrated based on the calibrated value.
The output of 3 may be controlled.

Furthermore, when applying a high voltage to the photoreceptor drum 21 for output calibration of the potential sensor 24, the developing high voltage unit 3
The high voltage may be applied from the main high voltage unit 33 instead of 4.

Note that the present invention is not limited to the above-described copying machine, but can be similarly applied to other image forming apparatuses such as laser printers and electrophotographic facsimiles.

<Effects of the Invention> As described above, according to the present invention, a potential sensor that detects the surface potential of a photoreceptor and a circuit that automatically calibrates the output of the potential sensor are provided, and a potential sensor whose output is calibrated is provided. Since the charger is controlled so that the surface potential of the photoconductor is charged to a constant potential based on the measured value of It is possible to form beautiful images.

Further, according to the present invention, when an abnormality occurs in the image forming apparatus and the image forming apparatus is stopped and then restarted, even if there is a residual charge on the photoreceptor due to the abnormal stop. Since the potential sensor is calibrated after the residual charge is completely removed, the apparatus can always perform accurate calibration.

Furthermore, since the high voltage generation circuit is also used as a circuit for biasing the developing device or for applying voltage to the charger, the number of components does not increase.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a control circuit according to an embodiment of the present invention. FIG. 2 is a schematic mechanical configuration diagram of the image forming mechanism of an electrophotographic copying machine according to an embodiment of the present invention. FIG. 3 is an operation timing diagram of the control circuit of FIG. 1. FIG. 4 is a flowchart for explaining the operation of the control section 35 of the control circuit shown in FIG. FIG. 5 is a graph showing the relationship between the voltage applied to the photosensitive drum 21 and the output of the potential sensor 24. In FIG. FIG. 6 is an illustrative diagram illustrating the relationship among a photosensitive drum, a developing roller, and a potential sensor of a conventional copying machine. In the figure, 21...photosensitive drum, 23...main charger, 24...potential sensor, 25...
Blank lamp, 3...Developing roller, 33...Main high pressure unit, 34...Developing high pressure unit, 35
・Control unit, 37...first changeover switch, three...relays are shown. Patent Applicant 3 1) Kogyo Co., Ltd. Chief brewer Rinto Patent attorney Hiroshi Kamei (and 2 others) No. 1 〒B〒] Control unit memory Memory/

Claims (1)

[Claims] 1. Opposing the photoconductor and the surface of the photoconductor countermeasure by performing corona discharge. Charge the facing photoreceptor surface to a constant potential. It has a charger that is charged to a constant potential. The surface of the photoreceptor is exposed to light. Image formation in which an electrostatic image is formed In the device, high voltage to output a predetermined high voltage. voltage generation circuit, The photoreceptor is connected to a high voltage generation circuit. Switch to switch between grounded and grounded means of Measuring the charged potential on the surface of the photoreceptor potential sensor for, Record that the image forming device has stopped abnormally. means of remembering, timing signal output means, When the timing signal is output, The storage means stores abnormal stoppage. If there is an abnormality, remove the static electricity from the photoconductor. If you do not remember to stop, immediately move forward. High voltage is directly applied to the photoreceptor from the high voltage generating circuit. the switch so that pressure is applied. A switching signal output that outputs a switching signal for the switching means. force means, and The photoreceptor is preset by a high voltage generation circuit. The potential sensor when the voltage is set to the specified high voltage. Based on the measured value of the charger, charger control means for controlling output; An image forming apparatus comprising: 2. In the image forming apparatus according to claim 1, There, The high voltage generation circuit is connected to a developing device bypass. It is also used as a high voltage generation circuit for Ru. 3. In the image forming apparatus according to claim 1, There, The high voltage generation circuit is connected to the charger. High voltage generation circuit for applying voltage and It is also used.